



5 plate. Thusgthewax acts as a lubricantgfor the press platen andentirely eliminates all sticking .and'platefouling problems. Also, theplates of the hot press may be treated with lubricants capableofwithstanding press plate temperatures to. prevent sticking or foulingproblems.

.If, a. highly finished, hard, .glossy surface is desired on the overlayin the. finished product, Ihave discovered that this result may beaccomplished by applying to the. upper surface of the preliminarilycompressed overlay as indicated. at

20 in Figure 2b, a thin coating of the same'synthetic resin as isemployed as the. binder the overlay .mixture. In some cases, the resinis mixed with an. equal volume of water and.

sprayed at the rate of 10. .lbs of resin per 1,030 square feet ofoverlay surface. In other cases, where a higher surface resin content isdesired, the resin may be used. without dilution. and

sprayed at the rate of 15 or more lbs. of resin per thousand feet.

As. a'result of this procedure, and others herein described, the overlayhas a relatively high concentration of resin on the outer surface and arelatively low resin concentration in the body, and a relatively highresin concentration at the line of junction with the plywood panel--thelatter being provided for by the preliminary treating of the panel, asdescribed above.

When the surface of the preliminarily compressed overlay is sprayed withresin, as just de-- scribed, more mold lubricant should be used, toprevent the material from sticking to the platen of the hot press. Thelubricant is preferably applied directly to the platen, but in somecases may be incorporated in the coating. The silicone material known asMold Release, sold by Dow Corning Company is satisfactory.

The final pressing operation may be performed in a. mulitple opening,steam heated hotpress l8 expanding gases to escape from the layer ofoverlay, without any danger of disruption thereof. Theoverlay materialis quite porous and includes a. great multiplicity of minute openings,betweenv the various wood particles. As the pressure is decreased, thegases created during the setting of the resin find their way throughthese pores or openings to the surface, and readily escape as thepressure approaches 'zero and while the platen is still in contact withthe outer surface of the overlay.

Thus, the entire pressing cycle in the final pressing operation may bemaintained as low as substantially three .minutes, depending on thethickness of the overlay and the temperatures and pressures employed.

After the panels are removed from the hot press, the moisture content ofthe plywood portion'is often unduly low, because of the extra pressingoperation to which it has been subjected. Hence, it is desirable tocondition the panels. This conditioning operation may be readilyaccomplished by subjecting the individual panels to currents of moistair for a suitaibleperiod of time to permittherplywdod tuabsorb.sufficient .moi'stureqto its content: up

. from warping bending or cupping under variations in the moisturecontent .ofthepanel, such *as occurtiwhen the panel islater subject.to-jordinary variations in the humidityl'of the surroundingadmo'sphere. Plywood having my overlay cnzone face only has the samecharacteristics', so far as warping, :etc., as the plywood itself."This-ability toprovide the overlay on one surface only of the panel isan advantage of major commercial importance, since, in many usesofplywood panels, only one face is exposed, and. the appearance of theback face is a matter of complete indifference.

With plywood overlay materials in accordance with the prior art, it hasbeen impossible, commercially, to produce panels having the overlay ononly on surface, because of the resulting warping, cupping or otherdistortions in shape. For instance, with resin impregnated paper sheetoverlays or the like, manufacturers have. been forced, in the commercialart, to apply the paper sheets or other fibrous webs to both faces ofthe panels, to prevent warping and bending thereof, irrespective of theuse'to which the panels were to be put, and in spite of the additionalcost of providing the extra overlay.

Although the technical explanation for these phenomena is not clearlyunderstood, it is thought that the relatively high tensile strength andtheimpervious character of the impregnated paper overlay materials giveto these materials very different expansion and contractioncharacteristics, under changes in moisture content than the veneerplies. Hence, the non-covered face of the plywood panel may absorb andgive up moisture more rapidly than the covered face, with a resultingdifference in expansion and contraction on the two faces of the panel.Moreover, even if all of the wood plies absorb the same amount ofmoisture and tend to expand equally, the impregnated paper overlay,bonded to one surface, .has such a tensile strength that the lattersurface and the wood bonded to it cannot expand with the balance of thewood, and the panel warps and curves badly upon changes in moisturecontent.

With an overlay produced in accordance with the present invention,however, the layer of discrete wood particles and synthetic resin isquite porous and has a low tensile strength. Hence,

moisture can permeate through the overlay so that both faces of thepanel absorb and give up moisture at substantially the same rate.Apparently, the wood particles in the overlay itself absorb and give upmoisture so that they expand and contract with the plywood part of thecomposite panel. Also, since the wood particles in the overlay are notinterlaced, entwined and felted together, as in the case with the libersin paper-like sheets or fibrous webs, they are not sufficientlyinterlocked to prevent slight movements between the fibers and equalexpanscribed with particular reference to applying overlay materials toplywood panels, it must be understood that it is not limited thereto, asthe novel procedures are of utility in applying overlays to other typesof wood products, such as conventional lumber, as individual pieces orassembled into larger sheets or panels. Thus, the novel steps of coatingthe surface of the wood product with a thin coating of synthetic resin,applying the overlay to the coated surface, preliminarily compressingthe overlay, applying a surface coating of resin to the preliminarilycompressed mixture, and finally compressing the overlay under suiiicientheat and pressure to convert the resin, may be employed for otherpurposes than providing an improved overlay on plywood.

I claim:

1. The method of making a wood product having an overlay thereon, whichcomprises applying to the surface of a wood sheet, a smooth, even layerof substantial thickness of a mixture of discrete wood particles andan'aqueous synthetic resin solution, preliminarily compressing the layerunder heat of at least substantially 250 F.

and under pressure of at least substantially 30 pounds per square inch,for at least seconds and completely releasing said preliminarycompressing, thereby compacting the mixture sufficiently to preventaccidental disturbance of the layer during subsequent handling, andsubsequently subjecting the wood sheet and the layer to greater heat andpressure for a longer time to compact the layer and to convert the resinto the insoluble, infusible state and to bond the Wood particles to eachother and the layer as a whole to the surface of the wood sheet.

2. The method of making a wood product having an overlay thereon, whichcomprises applying to the surface of a wood sheet, a smooth, even layerof substantial thickness of a mixture of discrete wood particles and anaqueous synthetic resin solution, preliminarily compressing the layerunder heat of at least substantially 250 F. and under pressure of atleast substantially 30 pounds per square inch, for at least 5 seconds tocompact the mixture and to prevent accidental disturbance of the layerduring subsequent handling, completely releasing said preliminarycompression and the application of heat, subsequently subjecting thewood sheet and the layer to greater heat and final pressure for a longertime to compact the layer and to convert the resin to the insoluble,infusible state and to bond the wood particles to each other and thelayer as a whole to the surface of the Wood sheet,

and gradually reducing the final pressure, to

permit the gradual escape of steam from the layer before entirelyreleasing the final pressure.

3. The method of making a plywood product having an overlay thereon,which comprises applying to at least one surface of the panel a thincoating of an aqueous synthetic resin solution, applying to the coatedsurface of the panel a smooth even layer of substantial thickness of arelatively dry mixture of discrete wood particles and an aqueoussynthetic resin solution which is similar to and compatible with theresin of said coating, preliminarily compressing the layer under heatand pressure, completely releasing the preliminary application ofpressure and heat after sufficient time and temperature to compact themixture sufficiently to prevent accidental disturbance of the layerduring subsequent handling of the panel, and subsequently subjecting thepanel and the layer to greater heat and pressure for a longer time toconvert the resins to substantially the insoluble, infusible state andto bond the wood-particles to each other and the layer as a whole to thesurface of the panel.

4. The method of making a plywood product having an overlay thereon,which comprises applying to the surface of the panel a smooth, evenlayer of substantial thickness of a mixture of discrete wood particlesand an aqueous synthetic resin solution, preliminarily compressing thelayer under heat and pressure, completely releasing thepreliminaryapplication of pressure and heat after sufiicient time and temperatureto compact the mixture suificiently to prevent accidental disturbance ofthe layer during handling and to provide a substantially smooth,continuous, uniform upper surface on the layer, applying to the uppersurface of the preliminarily compressed layer, a coating of an aqueoussolution of a synthetic resin similar to the resin in said mixture andthereafter subjecting the panel, the layer and the coating to greaterheat and pressure for a longer time to convert the resins tosubstantially the insoluble, infusible state and to bond the woodparticles to each other and the layer as a Whole to the surface of thepanel.

5. The method of making a plywood product having an overlay thereon,which comprises applying to a surface of the panel a thin coating of anaqueous synthetic resin solution, applying to the coated surface of thepanel a smooth, even layer of substantial thickness of a mixture ofdiscrete wood particles and an aqueous synthetic resin solution which issimilar to and compatible with the resin of said coating, preliminarilycompressing the layer under heat and pressure, completely releasing thepreliminary application of pressure and heat after suffic-ient time andtemperature to compact the mixture suiiiciently to prevent accidentaldisturbance of the layer during subsequent handling, applying onto thesurface of the preliminarily compressed layer a coating of an aqueoussolution of a synthetic resin similar to the resin used in the mixture,and thereafter subjecting the panel, the layer and said coating togreater heat and pressure for a longer time to convert the resin tosubstantially the insoluble, infusible state and to bond the woodparticles to each other and the layer as a whole to the surface of thepanel.

6. The method of making a plywood product having an overlay thereon,which comprises applying to the surface of the panel a smooth, evenlayer of substantial thickness of a mixture of discrete wood particlesand an aqueous synthetic resin solution, preliminarily compressing thelayer on the panel for from 5 to 10 seconds at 250 to 300 F.,'to compactthe mixture sufficiently to prevent accidental disturbance of the layerduring subsequent handling, completely releasing said preliminarycompressing, and subsequently subjecting the panel and the layer to

1. A COMPOSITION COMPRISING N-VINYL CARBAZOLE ANDTETRAETHYLPYROPHOSPHATE.